For diagnostic examination and for interventional procedures, e.g. in cardiology, radiology and also neuro-surgery, interventional x-ray systems are used for imaging, the typical major features of which can be for example be a robot-controlled C-arm to which an x-ray tube and an x-ray detector are attached, a patient support table, a high-voltage generator for generating the tube voltages, a system control unit and a display system including at least one monitor. This type of C-arm x-ray system, which is shown by way of example in FIG. 1, typically features a C-arm 2 supported rotatably on a stand in the form of a six-axis industrial or articulated-arm robot 1, attached to the ends of which are an x-ray source, for example an x-ray tube unit 3 with x-ray tubes and collimators, and an x-ray image detector 4 as an imaging unit.
By means of the articulated-arm robot 1 known for example from DE 10 2005 012 700 A1, which preferably has six axes of rotation and thereby 6 degrees of freedom, the C-arm 2 can be adjusted spatially as required, for example by being turned around the center of rotation between the x-ray tube unit 3 and the x-ray detector 4. The inventive x-ray system 1 to 4 is especially able to be rotated around centers of rotation and axes of rotation in the C-arm plane of the x-ray image detector 4, preferably around a center point of the x-ray image detector 4 and around the center point of the axes of rotation intersecting with the x-ray image detector 4.
The known articulated-arm robot 1 has a base support which is mounted fixed on a floor for example. A carousel able to be rotated around a first axis of rotation is attached rotatably thereto. Attached to the carousel pivotably around a second axis of rotation is a robot motion link to which a robot arm is attached rotatably around a third axis of rotation. A robot hand is attached at the end of the robot arm rotatably around the fourth axis of rotation. The robot hand has an attachment element for the C-arm 2 which is able to be pivoted around a fifth axis of rotation and is rotatable around a sixth axis of rotation running at right angles thereto.
The realization of the x-ray diagnostic device is not dependent on industrial robots Normal C-arm devices can also be used.
The x-ray image detector 4 can be a rectangular or square, flat semiconductor detector which is preferably made of amorphous silicon (a-Si). Integrating and possibly scanning CMOS detectors can also be used.
Located as an examination object on a patient support table 5 in the beam path of the x-ray tube unit 3, for recording an image of a heart for example, is a patient 6 to be examined. Connected to the x-ray diagnostic device is a system control unit 7 with an image system 8 which receives and processes the image signals of the x-ray image detector 4 (control elements are typically not shown). The x-ray images can then be viewed on a monitor 9.
An important method of interventional radiology is the so-called roadmap method. In this method, as is explained with reference to FIG. 2, in a mask phase A, a mask image 13 is initially created which contains the contrast medium-filled vascular tree 14. In such cases one or more x-ray images are recorded which produce x-ray images without filling, so-called empty images 10. Subsequently further x-ray images are detected after contrast media have been injected, so-called fill images 11.
The mask image 13 is determined by means of a mask computation from the empty 10 and fill images 11 12 as mask M(i,j). Usually the various x-ray images (Bk(i,j) k=1,K) are averaged using fluoroscopic, i.e. small, doses. The known moving weighted averaging can be used for this purpose, in which a percentage of the previous image is overlaid with the current image—possibly coupled to a movement detector.
If necessary, for improved display of the vascular tree 14, an “opacity” method is used, i.e. the respective darkest value of a pixel from all x-ray images is used in the mask image 13. The image frequency is usually the same as during the roadmap phase B, in which the mask image 13 is subtracted from a fluoroscopy image 15 Bl l=1,L in which an object, typically a wire, a catheter 16 or a “coil” is moved in a vessel of the vascular tree 14. Through this subtraction 17 all anatomical (immobile) structures are subtracted and the filled vascular tree 14—now shown in “white” by the subtraction—and the catheter 16 are left. This greatly reduces the image contrast and vascular tree 14 and catheter 16 are sensibly visible in roadmap images 19 RMl(i,j), l=1,L. In mask phase A no contrast medium is added but the anatomy is simply recorded. In the roadmap phase B adhesives are then introduced by means of a catheter 16 at the point to be embolized. The course of the adhesive is followed in this roadmap phase B. By subtraction 17 of the mask image 13 which only contains the anatomy from the image series 15 with adhesives and the anatomy and if necessary subsequent image processing 18, only the adhesive remains, the course of which can now be shown in very high contrast in roadmap images 19 RMl(i,j), l=1,L.
The previous method has a few disadvantages:                The generation of the mask image (mask phase A) takes up to two seconds. This depends amongst other things on the image rate and the image post processing steps (such as the averaging method). The user (generally the radiologist) would like however, especially for embolizations, to see practically instantly how strongly the adhesive is running or whether it has already begun to harden and is no longer running.        The averaging method (moving weighted average) reduces the maximum possible contrast of the contrast medium during the mask phase A in the smallest vessels (where the contrast medium only arrives during the last recordings within the series of x-ray image 10 and 11).        